Apparatus and method for bending and/or tempering glass

ABSTRACT

An apparatus and method for bending and/or tempering glass substrate(s) are provided. The amount of near-IR radiation which reaches the glass to be bent and/or tempered is limited (e.g., via filtering or any other suitable technique). Thus, the IR radiation (used for heating the glass) which reaches the glass to be bent and/or tempered includes mostly mid-IR and/or far-IR radiation, and not much near-IR. In such a manner, coating(s) provided on the glass can be protected and kept at lower temperatures so as to be less likely to be damaged during the bending and/or tempering process. Heating efficiency can be improved. A ceramic (e.g., aluminosilicate) filter or baffle may be used in certain embodiments in order to reduce the amount of mid-IR and/or far-IR radiation reaching the glass to be tempered and/or bent.

This is a continuation-in-part (CIP) of U.S. patent application Ser. No.10/101,516, filed Mar. 20, 2002, the disclosure of which is herebyincorporated herein by reference.

This invention relates to an apparatus and method for heat bendingand/or tempering glass sheets. More particularly, this invention relatesto an apparatus and method for bending and/or tempering glass sheets bydirecting infrared (IR) radiation at the glass sheet(s) in order to heatthe same, wherein the IR radiation is filtered or otherwise adjusted soas to have more radiation in the mid-IR and/or far-IR ranges than in thenear IR-range.

BACKGROUND AND SUMMARY OF THE INVENTION

Devices and methods for heat bending glass sheets are well known in theart. For example, see U.S. Pat. Nos. 5,383,990; 6,240,746; 6,321,570;6,318,125; 6,158,247; 6,009,726; 4,364,766; and 5,443,669.

FIG. 1 is a schematic diagram illustrating a conventional apparatus andmethod for heat bending glass sheets in making a laminated product suchas a vehicle windshield. Vehicle windshields are typically curved, andthus require first and second curved (as a result of heat bending) glasssheets laminated to one another via a polymer interlayer. First glasssubstrate 1 has a multi-layer solar control coating 3 thereon (e.g.,low-E coating including at least one IR reflecting layer of a materialsuch as Ag); while second glass substrate 5 is not coated.

Referring to FIG. 1, two flat glass substrates 1, 5 are placed in abending furnace (e.g., on a bending mold) in an overlapping manner byinterposing an optional lubricating powder (not shown) such as sodiumhydrogen carbonate, cerite, magnesium oxide, silica, or the like betweencontacting surfaces of the two glass substrates. The glass substrates 1,5 are then heated using infrared (IR) emitting heating elements 7 to aprocessing temperature(s) near a softening point of the glass (e.g.,from about 550 to 850 degrees C., more preferably from about 580 to 750degrees C.) in order to soften the overlapping glass substrates 1, 5.Upon softening, the glass substrates 1, 5 (including any solar controlcoating 3 thereon) are bent by their deadweight (i.e., sagging) along ashaping surface of a bending mold (not shown) into the desired curvedshape appropriate for the vehicle windshield being made. A press bendingapparatus may optionally be used after the glass is sufficientlysoftened (the press bending may be conducted as the final step beforecooling the glass).

After being heat bent in such a manner, the bent glass substrates 1, 5(with solar control coating 3 still on substrate 1) are separated fromone another and a polymer inclusive interlayer sheet (e.g., PVB) isinterposed therebetween. The glass substrates 1, 5 are then laminated toone another via the polymer inclusive interlayer 9 in order to form theresulting vehicle windshield shown in FIG. 2.

Different vehicle windshield models require different shapes. Someshapes require more extensive bending than others. As windshieldsrequiring extensive bending are becoming more popular, the need for highperformance solar control coatings (e.g., including one or more IRreflecting Ag layers) has also increased. An example high performancesolar control coating 3 is disclosed in WO 02/04375 (and thuscounterpart U.S. Ser. No. 09/794,224, filed Feb. 28, 2001), both herebyincorporated herein by reference.

Unfortunately, it has been found that when using conventional glassbending techniques, certain solar control coatings cannot on a regularbasis withstand the bending process(es) sometimes used. Set forth belowis an explanation as to why certain solar control coatings have a hardtime withstanding conventional heat bending processes without sufferingundesirable damage such as reduced transmission.

Conventional glass bending heating elements emit IR radiation 8 in thenear, mid and far IR ranges. By this we mean that heating elements 7emit each of near-IR (e.g., 700–4,000 nm; or 0.7 to 4.0 μm), mid-IR(4,000–8,000 nm; or 4–8 μm), and far-IR (>8,000 nm; or > 8 μm)radiation. In certain instances, the near-IR range may be consideredfrom 0.7 to 3.0 μm and the mid-IR range from 3–8 μm. Herein, IRradiation is defined as wavelengths of 0.7 μm and above with knownconstraints.

Each of these different types (i.e., wavelengths) of IR radiationimpinges upon the glass substrates 1, 5 to be heated and bent. CertainIR radiant heaters work in a manner such that turning up the power forthe same results in significantly more near-IR radiation being emitted.In any event, much of the IR radiation from conventional heaters thatreaches the glass to be bent is in the near-IR range, as the peak ofthis IR radiation is often in the near-IR range. In certain exampleinstances, at least about 50% of the IR radiation that reaches the glassto be bent is in the near-IR range, sometimes 70% or higher. Forinstance, a heater with black body properties operating at 538 degreesC. emits 32.8% of its energy from 0.7 to 4 μm, 44.7% from 4 to 8 μm and22.5% in wavelengths greater than 8 μm. A heater with black bodyproperties operating at 871 degrees C. emits 57.6% of its energy from0.7 to 4 μm, 31.9% from 4 to 8 μm and 10.5% in wavelengths greater than8 μm. A heater with black body properties operating at 1,094 degrees C.emits 68.7% of its energy from 0.7 to 4 μm, 24.4% from 4 to 8 μm and6.9% in wavelengths greater than 8 μm. The total power emitted increaseswith temperature proportional to the absolute temperature raised to thefourth power. For the three temperatures listed above, the total emittedpower is approximately 15, 63 and 125 watts/inch square, respectively.The power for 0.7 to 4 μm is 4.9, 36.3, and 85.9 watts/inch square,respectively.

U.S. Pat. No. 6,160,957 discloses a heating element including a resistorelement mounted on a ceramic fiber material such as aluminosilicate inspaced relation thereto. However, in the '957 Patent it is the resistorelement (not the ceramic fiber) which emits the IR radiation toward theproduct to be heated.

As shown in FIG. 3, it has been found that typical soda lime silicaglass (often used for substrates 1, 5) has a high absorption of IRradiation in the mid-IR and far-IR ranges. In other words, soda limesilica glass absorbs much of incident IR radiation at wavelengths aboveabout 3–4 μm (microns). Thus, in the mid and far-IR ranges, the glassabsorbs much of the IR radiation before it can reach the coating. It isbelieved that this absorption in the mid and far-IR ranges is due to atleast water, Si—O and Si—O—H absorption in the glass matrix. FIG. 3shows that soda lime silica glass is substantially opaque to IRradiation above 3–4 μm, but rather transmissive of IR radiation below3–4 μm. Unfortunately, the transmissive nature of the glass atwavelengths less than 3–4 μm means that a significant amount of IRradiation in the near-IR range (from 0.7 to 3–4 μm) is not absorbed bythe glass substrate(s) 1 and/or 5 and as a result passes therethroughand reaches solar control coating 3. As used herein, the phrase “from0.7 to 3–4 μm” means from 0.7 μm to 3 and/or 4 μm. The amount of energyin this wavelength band (watts/inch²) increases as the temperature ofthe elements increases. Typically, the power applied in later times inthe bending process is substantially higher than earlier times so thatthe amount of energy not absorbed by the glass and thus by the coatingincreases as the bending process proceeds.

Unfortunately, certain of this near-IR radiation which is not absorbedby the glass substrate and thus reaches solar control coating 3, isabsorbed by the coating 3 (e.g., by Ag layer(s) of the coating) therebycausing the coating 3 to heat up. This problem (significant heating ofthe coating) is compounded by: (a) certain solar control coatings 3 havea room temperature absorption peak (e.g., of 20–30% or more) atwavelengths of approximately 1 μm in the near IR range, at whichwavelengths the underlying glass is substantially transmissive, and (b)the absorption of many solar control coatings 3 increases with a rise intemperature thereof (e.g., sheet resistance R_(s) of Ag layer(s)increase along with rises in temperature). In view of (a) and (b) above,it can be seen that the peak absorption of certain solar controlcoatings 3 at near-IR wavelengths of about 1 μm can increase from the20–30% range to the 40–60% range or higher when the coating temperatureincreases from room temperature to 500 degrees C. or higher, therebyenabling the coating to heat up very quickly when exposed to significantamounts of near-IR wavelengths. The temperature of the coating may bemitigated by conduction of the absorbed energy into the bulk glass, butthe rate of this process is finite. If energy is applied to the coatingfaster than it can be dissipated into the bulk, a thermal gradient iscreated leading to substantial overheating of the coating which leads tocoating damage. The potential for coating overheating is often highestin the later stages of the bending process when the glass and coatingare near the softening point, e.g., due to the higher amounts of near-IRheat being generated by the heating element(s) and due to absorption ofthe coating being higher.

Coating 3 is more susceptible to being damaged when it is unnecessarilyheated up during the glass bending process. When coating 3 is damaged(e.g., visible transmittance drops significantly), the bent glasssubstrate 1 with the damaged coating thereon is typically discarded andcannot be commercially used.

This problem (i.e., coating overheating) also affects the shapes thatcan be attained in the bending process. If heat is applied only from oneside (e.g., from the top in FIG. 1), the presence of the coating onsubstrate 1 versus substrate 5 limits the radiant energy that can beabsorbed by the substrate 5; so the substrate 1 may become more softthan substrate 5. This means that substrate 1 must often be overheatedin order to enable substrate 5 to reach a desired temperature forsagging to a desired shape. Application of heat to both the top andbottom (see FIG. 1) provides radiant heat directly to both substrates,but also causes the coating to receive double the amount of energypotentially leading to overheating.

It can be seen that certain solar control coatings 3 have a narrowthermal stability range that can limit the shape (i.e., degree ofbending) of glass attainable in a bending process. Highly bentwindshields often require higher bending temperatures and/or longbending times which certain coatings 3 cannot withstand givenconventional glass bending techniques.

An object of this invention is to minimize the time at and/or peaktemperature attained by a solar control coating 3 during a heat bendingprocess for bending and/or tempering a glass substrate that supports thecoating.

Another object of this invention is to provide an apparatus and/ormethod for heat bending and/or tempering glass substrates/sheets,designed to reduce the amount of near-IR radiation that reaches theglass substrate(s) to be bent.

Another object of this invention is to provide a filter (or baffle) forfiltering out at least some near-IR radiation before it reaches a glasssubstrate to be bent and/or tempered. This can enable a solar controlcoating supported by the glass substrate to reach a lesser temperaturethan if the filter was not provided.

By enabling the maximum coating temperature to be reduced (and/or thetime at which the coating is at a maximum temperature to be lessened),certain embodiments of this invention can realize one or more of thefollowing advantages: (a) the solar control coating is less likely to bedamaged during the bending and/or tempering process of an underlyingglass substrate, (b) higher degrees of bending of an underlying glasssubstrate can be achieved without damaging the solar control coating;(c) heating time and/or maximum coating temperature can be reducedwithout reducing the amount of glass bend, and/or (d) power consumptionof the heater may be reduced in certain instances.

In certain example embodiments of this invention, a filter (e.g., baffleor the like) of or including a ceramic (e.g., a silicate such asaluminosilicate) is used which reduces the amount near-IR radiationwhich reaches the glass substrate and/or coating to be bent and/ortempered.

Another object of this invention is to fulfill one or more of theabove-listed objects.

In certain example embodiments of this invention, one or more of theabove-listed objects is/are fulfilled by providing an apparatus forbending and/or tempering a glass substrate, the apparatus comprising: aheating element for generating energy; and a near-IR filter comprising aceramic radiating surface located between the heating element and theglass substrate, the near-IR filter for reducing the amount of near-IRradiation that reaches the glass substrate to be bent and/or tempered.

In other example embodiments of this invention, one or more of theabove-listed objects is/are fulfilled by providing a method of bendingglass, the method comprising: providing a glass substrate having a solarcontrol coating thereon; directing IR radiation at the glass substratefrom a heating layer comprising ceramic in order to heat the glasssubstrate to a temperature of at least about 550 degrees C. for bending;and wherein less than about 30% of the IR radiation reaching the glasssubstrate is at wavelengths from 0.7 to 3.0 μm.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of a conventional apparatus and method forbending glass sheets.

FIG. 2 is a cross sectional view of a vehicle windshield made using theapparatus and method of FIG. 1.

FIG. 3 is a graph (wavelength vs. absorption) illustrating theabsorption of IR radiation by a piece of soda lime silica glass as afunction of wavelength.

FIG. 4 is a schematic diagram illustrating an apparatus and method forbending and/or tempering glass substrate(s)/sheet(s) according to anexample embodiment of this invention.

FIG. 5 is a flowchart illustrating certain steps taken in bending glasssubstrate(s)/sheet(s) according to an example embodiment of thisinvention.

FIG. 6 is a graph (wavelength vs. relative amount) illustrating thatmore mid-IR and/or far-IR heating radiation, than near-IR, reaches glasssubstrate(s) to be heated in the FIG. 4–5 and 7 embodiments of thisinvention.

FIG. 7 is a schematic diagram illustrating an apparatus and method forbending and/or tempering glass substrate(s)/sheet(s) according toanother example embodiment of this invention.

FIG. 8 is a cross sectional view of an example near-IR filter forfiltering out at least some near-IR wavelengths, that may be used in theFIG. 4–5 embodiments of this invention.

FIG. 9 is a schematic diagram illustrating an apparatus and method forbending and/or tempering glass substrate(s)/sheet(s) according toanother example embodiment of this invention.

FIG. 10 is a schematic diagram illustrating a silicate inclusive filterwhich may be used in an apparatus and/or method for bending and/ortempering glass substrate(s)/sheet(s) according to any of theembodiments of this invention.

FIG. 11 is a heating time vs. degree of glass substrate bendingcurvature graph illustrating that the silicate inclusive filters of theFIG. 10 embodiment enable a higher degree of glass bending to beachieved at a given temperature and heating time, compared to if thesilicate inclusive filters were not used.

FIG. 12 is an emissivity vs. wavelength graph illustrating the normalemissivity of an aluminosilicate filter in accordance with the FIGS.10–11 embodiment.

DETAILED DESCRIPTION OF EXAMPLE EMBODIMENTS OF THE INVENTION

Referring now more particularly to the accompanying drawings in whichlike reference numerals refer to like parts throughout the severalviews.

FIG. 4 is a schematic diagram of an apparatus and method for bendingand/or tempering glass substrates/sheets according to an exampleembodiment of this invention. Glass sheets or substrates bent and/ortempered herein may be used in applications such as vehicle windshields,other types of laminated or monolithic windows, IG window units, or anyother suitable application.

Referring to FIG. 4, first and second approximately flat glasssubstrates 1 and 5 are provided. First glass substrate 1 may have amulti-layer solar control coating 3 thereon (e.g., a low-E coatingincluding at least one IR reflecting layer of a material such as Ag,NiCr, Au or the like). Second glass substrate 5 may or may not be coatedin a similar manner. Coating 3 is provided on the side of substrate 1closest to the other substrate 5 in order to having the coating 3between lites after lamination. The glass substrates 1, 5 may be of orinclude soda lime silica glass, or any other suitable type of glass.

Example solar control coatings 3 are disclosed in U.S. Ser. No.09/794,224 filed Feb. 28, 2001 (see WO 02/04375), and in U.S. Pat. Nos.5,229,194; 5,298,048; 5,557,462; 3,682,528; 4,898,790; 5,302,449;6,045,896; and 5,948,538, all hereby incorporated herein by reference.While these are examples of solar control coatings 3 which may be used,this invention is not so limited as any other suitable solar controlcoating may instead be used. In certain embodiments of this invention,solar control coating 3 includes at least one IR reflecting layer (e.g.Ag, Au or NiCr) sandwiched between at least first and second dielectriclayers. In certain embodiments, the solar control coating 3 includesfirst and second IR reflecting layers (e.g., of or including Ag, Au orthe like), and a first dielectric layer (e.g., of or including siliconnitride, silicon oxide, titanium oxide or the like) provided between theunderlying glass substrate 1 and the first IR reflecting layer, a seconddielectric layer provided between the two IR reflecting layers, and athird dielectric layer provided over both IR reflecting layers (e.g.,see WO 02/04375 and 09/794,224). In certain embodiments of thisinvention, coating 3 may be deposited onto glass substrate 1 in anysuitable manner (e.g., via sputtering as described in any of theaforesaid patents/patent applications).

Referring to FIGS. 4–5 for example bending embodiments, approximatelyflat glass substrates 1 (with coating 3 thereon) and 5 may be placed ina bending furnace in an overlapping manner by interposing an optionallubricating powder (not shown) such as sodium hydrogen carbonate,cerite, magnesium oxide, silica, or the like between contacting surfacesof the two glass substrates. Coating 3 is between the substrates, andsupported by substrate 1 and/or 5. Heating elements 7 (e.g., aboveand/or below the glass substrates 1, 5) emit IR radiation 8 toward theglass substrates 1, 5 in order to heat the same for purposes of bending(see step A in FIG. 5). In certain embodiments of this invention,heating elements 7 emit IR radiation 8 in each of the near-IR, mid-IRand far-IR ranges; although in other embodiments the heating elements 7need not emit radiation in the mid or far-IR range. Near IR filter(s) 12filter out at least some of the near-IR rays (e.g., at some rays from0.7 to 3–4 μm) from the radiation before the radiation reaches the glasssubstrates 1, 5 (see step B in FIG. 5). Thus, the radiation 10 emittedand/or transmitted from filter(s) 12 includes less near-IR radiation(i.e., rays from 0.7 to 3–4 μm) than does the radiation 8 received byfilter(s) 12. IR radiation 10 emitted and/or transmitted from filter(s)12 may include both mid-IR and far-IR radiation in certain embodimentsof this invention, but need not include mid-IR radiation in allembodiments (see step C in FIG. 5). In different embodiments of thisinvention, filter(s) 12 may either be an integral part of the heatingelement 7, or alternatively may be spaced from the heating element 7 soas to be located between the substrate to be heated and the heatingelement 7 as shown in FIG. 4.

In certain embodiments of this invention, near-IR filter(s) 12 filtersout at least about 10% of the near-IR radiation from radiation 8, morepreferably at least about 30%, even more preferably at least about 50%,and most preferably at least about 70%. In certain embodiments of thisinvention, the radiation 10 which reaches glass substrates 1, 5 forheating the same includes IR radiation of which less than about 50% isin the near-IR range, more preferably less than about 30%, even morepreferably of which less than about 20% is in the near-IR range, stillmore preferably of which less than about 10% is in the near-IR range,and most preferably of which from about 0–5% is in the near-IR range.

The ratio of near-IR to far-IR emitted from heating element(s) 7 inradiation 8, for example, may be a function of heating elementtemperature as discussed above. As explained above, this ratio of nearto far-IR emitted from heating element(s) 7 may be about 1.4 at 538degrees C., about 5.5 at 871 degrees C. and about 10 at 1093 degrees C.In certain embodiments of this invention, the near-IR filter(s) reducesthis ratio at a given temperature to less than 85%, more preferably lessthan 50%, and most preferably less than 35% of its original value. Incertain embodiments, the filter(s) does not attenuate the mid and/or farIR radiation by more than 50% of its original value, more preferably notmore than 20% of its original value. This enables a significant amountof near-IR to be filtered out, while maintaining a relatively high poweroutput in the mid and/or far IR bands.

Because of the reduced amount of near-IR radiation reaching glasssubstrates 1, 5, the substrates can absorb more of the IR radiation(i.e., since the glass absorbs significant IR radiation in the mid andfar-IR regions) and less IR radiation reaches coating 3. Because less IRradiation reaches coating 3, the coating 3 is not heated as much as itwould have been if filter(s) 12 were not provided. Stated another way,by heating the glass substrate 1 from the non-coated side thereof usingpredominantly mid and/or far IR wavelengths (and less or littlenear-IR), the coating 3 can be kept at a lower temperature and/or thetime period that the coating is at higher temperatures can be reduced.The ability to keep coating 3 at a lower temperature during bending ofthe underlying glass substrate 1 enables the coating 3 to be lesssusceptible to damage. Moreover, it will be appreciated that glass ismore efficiently heated using mid-IR and/or far-IR radiation (as opposedto near-IR) since the glass absorbs and is heated by radiation in themid and far-IR ranges. As a result, yields increase and more extremebending can be conducted. In other words, selecting how the glass isheated by predominantly using mid-IR and/or far-IR wavelengths (i.e.,wavelengths that the glass is substantially opaque to and absorbs) heatsthat glass in an efficient manner while simultaneously protecting thecoating 3.

During the bending process, the glass substrates 1, 5 are heated to aprocessing temperature(s) near a softening point of the glass (e.g.,from about 550 to 850 degrees C., more preferably from about 580 to 750degrees C.) in order to soften the overlapping glass substrates 1, 5.Upon softening, the glass substrates 1, 5 (including any solar controlcoating 3 thereon) are bent by their deadweight (i.e., sagging) along ashaping surface of a bending mold (not shown) or other suitablestructure into the desired curved shape. The glass sheets may optionallybe press bent after reaching an appropriate temperature. After beingheat bent in such a manner, the bent glass substrates 1, 5 (with solarcontrol coating 3 still on substrate 1) are separated from one anotherand a polymer inclusive interlayer sheet 9 (e.g., of or includingpolyvinyl butyral (PVB) or any other suitable laminating material) isinterposed therebetween. The bent glass substrates 1, 5 are thenlaminated to one another via the polymer inclusive interlayer 9 in orderto form a vehicle windshield or any other suitable structure (e.g., seeFIG. 2).

While FIG. 4 illustrates a pair of glass substrates 1, 5 being benttogether at the same time, this invention is not so limited. In certainalternative embodiments, the bending apparatus may bend only one glasssubstrate at a time. Moreover, bending techniques and/or methods hereinmay be used to bend glass substrates 1, 5 regardless of whether theyhave coatings thereon. The techniques described herein may also be usedin order to temper glass substrates (instead of or in addition tobending the glass); as the filter(s) 12 would also be useful in thermaltempering processes in order to keep the coating at as low a temperatureas possible while the underlying glass is tempered.

FIG. 6 is a graph illustrating an example spectrum of radiation 10 whichreaches the glass substrates 1 and/or 5 after being filtered byfilter(s) 12. As can be seen, the majority of radiation reaching theglass substrates 1 and/or 5 is in the mid-IR and far-ER ranges, withonly a small amount in the near-IR range. As explained above, thisenables the time and peak temperature attained by solar control coating3 during the heat bending process to be minimized; which in turn reducesthe likelihood of the coating being damaged.

FIG. 7 is a schematic diagram of another embodiment of this invention.The FIG. 7 embodiment is similar to the embodiment of FIGS. 4–5, exceptthat the IR heating element(s) 7 a are of a type that emits primarilymid-IR and/or far-IR radiation, and not much if any near-IR radiation.FIG. 6 illustrates an example spectrum of radiation that may be emittedby IR heating element(s) 7 a. The radiation 10 emitted by heatingelement(s) 7 a in the FIG. 7 embodiment is similar to that 10 afterfiltering in the FIG. 4–5 embodiment. Near-IR filter(s) 12 may or maynot be used in conjunction with the FIG. 7 embodiment. The radiationemitted by the heating elements 7 may be altered by the application ofan appropriate coating(s) to the heating element(s) surface in certainembodiments of this invention.

FIG. 8 is a cross sectional view of an example near-IR filter 12 whichmay be used in any of the FIGS. 4–7 embodiments of this invention. Inthis example, near-IR filter 12 (which filters out at least some near-IRradiation as discussed above) includes layers 20, 22 and 24. Layer 20acts as a substrate for the other layers and also functions as a heatinglayer in that it receives heat (e.g., in the form of IR radiation,conduction, or the like) from a heating element and transfers the heatto layer 22 via conduction. Layer 20 may or may not contact the heatingelement in different embodiments of this invention. If layer 20 is notin direct contact with the heating element(s), it may include anoptional layer or coating on its surface facing the heating element(s)that is a broad wavelength high emissivity coating to maximize theefficiency of capturing IR emitted from the heating element(s). Forexample, in the context of FIG. 4, layer 20 receives IR radiation 8 fromheating element 7 and as a result thereof heats up. Layer 20 may be ofor include Ni, Cu, Au, or any other suitable material capable of heatingup in such a manner in different embodiments of this invention.Alternatively, layer 20 may be heated by conduction resulting fromdirect contact with the heating element(s). Ni is a preferred materialfor layer 20 in view of its high melting point and its compatibilitywith Au that may be used for layer 22. Layer 20 may be any suitablethickness; in example non-limiting embodiments layer 20 may be of Nihaving a thickness of about ½ inch.

As heating layer 20 is heated up, it in turn heats up layer 22 (e.g.,via conduction heating when layers 20 and 22 are in contact with oneanother). Layer 22 is chosen to be of a material that has a lowemittance (low-E) in the near-IR range. In certain embodiments of thisinvention, layer 22 has an emissivity of no greater than about 0.5 inthe near IR range, more preferably no greater than about 0.3 in the nearIR range, still more preferably no greater than about 0.2 in the near IRrange, and even more preferably no greater than about 0.1 in the near IRrange. These example ranges in certain instances, may assume anemissivity of the unfiltered heater being from about 0.9 to 1.0. It canbe seen that near-IR range radiation reaching the glass to be heated canbe reduced when at a given wavelength the filter has an emissivity lessthan that of the heating element(s) 7. In certain embodiments of thisinvention, the emissivity of the total filter (e.g., layers 22, 24) isless than 80%, more preferably less than 50%, and most preferably lessthan 35% of the unfiltered heating element 7's emissivity. Layer 22 maybe of or include Au (gold), Ag (silver), Al (aluminum), or any othersuitable material in different embodiments of this invention. In certainexample embodiments, layer 22 is opaque and comprises Au from about200–20,000 Å thick. In alternative embodiments of this invention, layers20 and 22 may be combined in a single layer of a single material (e.g.,Au or any other suitable material).

High emissivity layer 24 (e.g., of or including fused silica) is heatedup by layer 22 via conduction, convective, and/or radiative heating. Incertain example embodiments, layer 24 may include at least about 75%SiO₂, more preferably at least about 80% SiO₂. Layer 24 may also includematerial such as aluminum oxide or the like. In certain embodiments,layer 24 has a rather high transparency of near-IR and a high emissivityin the mid and far IR regions; this may be achieved by a single layer ormultiple layers. Some absorption can be tolerated in the near IRspectrum of layer 24. Upon being heated by layer 22, layer 24 emits IRradiation (mostly in the mid and/or far-IR regions) 10 toward the glassto be bent; layer 24 has a rather high emittance for long IRwavelengths. In certain example embodiments of this invention, layer 24has an emissivity of at least about 0.4 at IR wavelengths of from 5 to 8μm, more preferably of at least about 0.45 at IR wavelengths of from 5to 8 μm, and even as high as 0.8 or higher for some wavelengths in therange of from 5 to 8 μm.

“Emissivity” is known as the measure of a material's ability to absorband/or emit radiation. For example, if a material has an emissivity of0.8 (out of 1.0), it radiates 80% of the energy that a perfect radiatorat the same temperature would radiate. Likewise, if a material has anemissivity of 0.1, it radiates only 10% of the energy that a perfectradiator at the same temperature would radiate. As for absorbtion, if amaterial reflects 20% of the electromagnetic energy striking it andabsorbs the other 80%, it has an emissivity of 0.8. Likewise, if amaterial reflects 90% of the electromagnetic energy striking it andabsorbs the other 10%, it has an emissivity of 0.1. If a material has anemissivity of 0.5, it will absorb 50% of the energy it intercepts andthe other 50% will either be reflected by it or transmitted through it.

As can be seen from the above, the near-IR filter of FIG. 8 is heated byheating element(s) 7 by for example conduction or convection, and emitsthe energy in a different form with less near-IR radiation compared tothe unfiltered radiation 8 from heating element(s) so that less near-IRradiation reaches the glass to be heated. The materials listed forfilter 12 are for purposes of example, and are not intended to belimiting unless specifically claimed.

FIG. 9 illustrates another embodiment of this invention, similar to anyone of those discussed above, except that a plurality of heatingelements (HE) 7 and a plurality of near-IR filters 12 are provided. Thefilters 12 are electrically and/or thermally insulated from one anotherto at least some extent (e.g., by spacing the filters from one anotherand having air or some other thermal insulator provided between thefilters). In such a manner, spatially distributed power (e.g., differentheat amounts being output from different heating elements 7) can be moreeasily controlled, so as to prevent thermal equalization among allfilters. In other words, if it is desired to heat one part of the glass(e.g., center) more than other parts of the glass (e.g., edges), thenmore power can be applied to the center heating elements 7. When this isdone in the FIG. 9 embodiment, the filters 12 near the center of theheating area filter out more near-IR than do the filters near the glassedges, but also emit more mid and/or far IR; so that even with thepresence of filters 12 the one part of the glass can still be heatedmore than other parts of the glass. This is advantageous when it isdesired to control bending to different shapes.

The aforesaid embodiments illustrate first and second heating elementsprovided on the top and bottom sides, respectively, of glass to be bent.However, this invention is not so limited, as in certain embodiments ofthis invention only a single heating element need by provided (eitherabove or below the glass to be bent).

FIG. 10 is a cross sectional view of another example near-IR filter 12which may be used in any of the aforesaid embodiments of this invention.In this embodiment shown in FIG. 10, filter(s) 12 may either be anintegral part of the heating element 7, or alternatively may be spacedfrom the heating element 7 so as to be located between the substrate tobe heated and the heating element 7. In either event, the filterincludes a radiating surface (of or including ceramic such as ceramicfibers) that directs heating radiation toward the substrate to be bentand/or tempered. In certain embodiments, there is no other structurebetween the substrate to be heated and the radiating surface as shown inFIG. 10.

It is noted that the heating element 7 is certain example embodimentsmay include a heater (e.g., metal or metal alloy coil/wire) mounted in amaterial such as a ceramic 7 a, coated with a black body or generallyblack coating 7 b as is known in the art. Example heating elements 7 areprovided in U.S. Pat. Nos. D452,561, 6,308,008, D449,375, 6,160,957,6,125,134, 5,708,408, 5,278,939, 4,975,563, 4,602,238, and 4,376,245,all incorporated herein by reference. However, any other suitable typeof heating element 7 may also be used, and this invention is not limitedto those listed above.

In the FIG. 10 embodiment, near-IR filter 12 (which filters out at leastsome near-IR radiation as discussed above) includes or is of a ceramicmaterial (e.g., oxide ceramic) at the radiating surface thereof. Incertain example embodiments, the filter 12 includes or is of a silicatesuch as aluminosilicate. The aluminosilicate in near-IR filter 12 may bein the form of a plurality of fibers in the form of a fiber board, or inany other suitable form including but not limited to a cloth comprisingfused silicate-inclusive fibers, Fiberfrax™, non-fiber ceramic, or thelike. It has been found that such a material has a very desirableemissivity (see FIG. 12) so that it does not emit much near-IRradiation. As a result, by using a filter(s) 12 of or including suchmaterial, the amount of near-IR radiation which reaches the glass andcoating to be bent/tempered is reduced compared to if the ceramicinclusive filter(s) was not used.

Referring to FIG. 10, the ceramic filter 12 may be in contact withheating element 7 or alternatively be spaced from the element 7 so as tobe located between the heating element 7 and the substrate 1 therebyacting as a sort of baffle as well as a filter. In either case, theceramic (e.g., aluminosilicate) inclusive filter 12 acts as a heatinglayer(s) in that it receives heat (e.g., in the form of IR radiation,conduction, convection, or the like) from heating element 7 and radiatesthe heat in rays 10 in accordance with the example emissivity shown inFIG. 12 so as to heat up substrate 1 for bending and/or tempering. Whilefilter 12 is shown in FIG. 10 as including only one layer, thisinvention is not so limited as other layer(s) may be provided infilter(s) 12.

The filter(s) 12 in the FIG. 10 embodiment (located above and/or belowthe glass to be heated) has an emissivity (e.g., see FIG. 12) whichcauses little near-IR radiation to reach the glass 1 to be heated. Incertain example embodiments of this invention, the emitting portion offilter(s) 12 has an emissivity of at least about 0.4 at IR wavelengthsof from 5 to 8 μm, more preferably of at least about 0.45 at IRwavelengths of from 5 to 8 μm, and most preferably as high as 0.7 (oreven 0.8) or higher for some wavelengths in the range of from 5 to 8 μm.Moreover, in certain example embodiments of this invention, the emittingportion of filter(s) 12 has an emissivity of less than 0.45 at allwavelengths from 0.9 to 3 μm, most preferably less than 0.35 at allwavelengths from 0.9 to 3 μm (e.g., see FIG. 12). Thus, filter 12 is ofa material(s) that emits an energy spectrum that is closelycoupled/related to the absorption spectra of soda lime silica glass(compare FIGS. 3 and 12). Moreover, in certain example embodiments ofthis invention, the material of the filter(s) may be selected so as tohave a total normal emissivity which is less at 650 degrees C. than at550 degrees C. (aluminosilicate fits this desire in certainembodiments).

In certain embodiments of this invention, ceramic fibers areparticularly useful as a material at the ceramic inclusive radiatingsurface shown in FIG. 10. This is because ceramic fibers tend to emitheating radiation toward the glass substrate to be bent and/or temperedin a diffused manner (as opposed to focused or collimated radiation). Incertain example embodiments of this invention, diffusion radiation forheating from a fiber-inclusive surface has been found to be particularlyadvantageous.

FIG. 11 illustrates example advantages of ceramic filter(s) 12 (whichmay also be used as baffle(s) in certain embodiments) noted in certainexamples according to the FIG. 10 and 12 embodiment of this invention.The FIG. 11 graph was made using aluminosilicate filters 12, althoughthe instant invention is not so limited. It can be seen that at a giventemperature (e.g., 590 degrees C.) and heating time, a greater degree ofcoated substrate bend can be achieved when the filter 12 of FIGS. 10, 12is used than if it is not used. This is because the emissivity offilter(s) 12 enables the glass to be more efficiently heated, comparedto if the filter(s) was not present.

While the invention has been described in connection with what ispresently considered to be the most practical and preferred embodiment,it is to be understood that the invention is not to be limited to thedisclosed embodiment, but on the contrary, is intended to cover variousmodifications and equivalent arrangements included within the spirit andscope of the appended claims.

1. An apparatus for bending and/or tempering a glass substrate, theapparatus comprising: a bending mold for supporting the glass substrateduring bending and/or tempering; a heating element for generating heat;and a near-IR filter comprising a ceramic inclusive radiating surfacelocated between the heating element and the glass substrate to be bentand/or tempered, the near-IR filter for reducing the amount of near-IRradiation that reaches the glass substrate to be bent and/or temperedduring the process of bending and/or tempering the glass substrate whenthe glass substrate is supported by the bending mold.
 2. The apparatusof claim 1, wherein the near-IR filter comprises a silicate.
 3. Theapparatus of claim 1, wherein the near-IR filter comprisesaluminosilicate.
 4. The apparatus of claim 1, wherein an emittingportion of the near-IR filter has an emissivity of at least about 0.4 atall IR wavelengths from 5 to 8 μm, and an emissivity of less than 0.45at all wavelengths from 0.9 to 3 μm.
 5. The apparatus of claim 1,wherein an emitting portion of the near-IR filter has an emissivity ofat least about 0.4 for at least some IR wavelengths in the range of from5 to 8 μm, and an emissivity of less than 0.45 for all wavelengths from0.9 to 3 μm.
 6. The apparatus of claim 5, wherein the emitting portionof the near-IR filter has an emissivity of at least about 0.7 for atleast some IR wavelengths in the range of from 5 to 8 μm, and anemissivity of less than 0.35 for all wavelengths from 0.9 to 3 μm. 7.The apparatus of claim 1, wherein the near-IR filter is spaced from theheating element and filters out at least about 30% of near-IR radiationreceived by the filter from the heating element.
 8. The apparatus ofclaim 7, wherein the near-IR filter filters out at least about 50% ofnear-IR radiation received by the filter from the heating element. 9.The apparatus of claim 1, wherein IR radiation output from the near-IRfilter which reaches and heats the glass substrate comprises less thanabout 50% near-IR radiation with the remainder of the IR radiation whichreaches the glass substrate being in the mid-IR and/or far-IR ranges.10. The apparatus of claim 1, wherein IR radiation output from thenear-IR filter which reaches and heats the glass substrate comprisesless than about 30% near-IR radiation with the remainder of the IRradiation which reaches the glass substrate being in the mid-IR and/orfar-IR ranges.
 11. The apparatus of claim 1, wherein IR radiation outputfrom the near-IR filter which reaches and heats the glass substratecomprises from 0–10% near-IR radiation with the remainder of the IRradiation which reaches the glass substrate being in the mid-IR and/orfar-IR ranges.
 12. The apparatus of claim 1, wherein at least the IRradiation output from the near-IR filter heats the glass substrate to atemperature of at least 550 degrees C.
 13. The apparatus of claim 1,further comprising another near-IR filter, wherein the near-IR filtersare on opposite sides of the glass substrate.
 14. The apparatus of claim1, wherein the near-IR filter is in contact with the heating element.15. An apparatus for bending and/or tempering a coated glass substrate,the apparatus comprising: means for bending and/or tempering the coatedglass substrate, the means including a heating element and a radiatingsurface comprising ceramic; wherein the radiating surface comprisingceramic is located between the heating element and the coated glasssubstrate, the radiating surface comprising ceramic for directingradiation toward the coated glass substrate in order to heat the coatedglass substrate for bending and/or tempering in a manner so as to reducethe amount of near-IR radiation that reaches the coated glass substrateto be bent and/or tempered.
 16. The apparatus of claim 15, wherein theradiating surface comprises a silicate.
 17. The apparatus of claim 15,wherein the radiating surface comprises aluminosilicate.
 18. Theapparatus of claim 1, wherein the near-IR filter comprises a radiatingsurface comprising ceramic fibers.
 19. The apparatus of claim 1, whereinthere is no heating structure between the radiating surface and theglass substrate to be bent and/or tempered.
 20. An apparatus for bendinga coated glass substrate, the apparatus comprising: a bending structurefor supporting the glass substrate during bending thereof; a heatingelement; and a radiating surface comprising ceramic located between theheating element and the coated glass substrate, the ceramic radiatingsurface for directing radiation toward the coated glass substrate inorder to heat the coated glass substrate for bending the glass substratethat is supported by the bending structure.
 21. The apparatus of claim20, wherein the radiating surface comprises ceramic fibers.
 22. Theapparatus of claim 20, wherein there is no heating structure between theradiating surface and the coated glass substrate to be bent.